New Study: Prosecutors, Not Police, Have Driven Prison Population Growth

The United States prison population has exploded over the past 40 years. But why? Have police been making more arrests? Have prosecutors been charging more people with crimes? Have judges been issuing longer sentences? Have parole boards become stricter? (All of the above?) Since many accounts of mass incarceration collapse “the criminal justice system” into a single monolith, it can be hard to know exactly what part of the system has driven the growth in the prison population.

A new empirical study by Fordham law professor John Pfaff aims to provide a more granular explanation of the causes of mass incarceration. Pfaff concludes that only one other relevant number has changed as dramatically as the prison population has: the number of felony case filings per arrest. In other words, police haven’t been arresting more people:

[B]etween 1982 and 1995, arrests rose by 26% (from 3,261,613 to 4,118,039) while mean [prison] admissions rose by 149% (from 212,415 to 530,642); between 1995 and 2007, arrests fell by 28.6% while admissions rose by another 31.9%. It is thus clear that arrests are not driving the growth in incarceration—and by extension neither are trends in crime levels, since their effect is wholly mediated by these arrest rates.

Rather, prosecutors have become more likely to charge those arrested with crimes:

[U]nlike the volume of arrests, that of felony case filings tracks the number of admissions quite closely. In the twenty‐six states that provide reliable felony filing data to the National Center on State Courts, between 1987 and 2006 filings grow by 129% (from 772,042 to 1,767,202) while admissions grow by an almost‐identical 132% (from 205,733 to 476,754). The decision to file charges thus appears to be at the heart of prison growth.

However, as Pfaff explains at length, this data doesn’t tell us whyprosecutors have been filing more charges per arrest. Did charging policies change, or did the pool of arrestees to whom those policies were applied change? One possibility is that, as crime rose from the 1960s through the 1990s, the people being arrested were more likely to have priors, making prosecutors more likely to charge them. But prosecutors have a lot of discretion, and to outside observers, their decision-making processes are a black box. Thus, Pfaff concludes by calling for more research into prosecutors’ offices: “While this paper does not resolve the causal question, it does tell us where precisely we need to look to find the correct causal answer(s).”

Intriguingly, while Pfaff discounts the War on Drugs as a direct driver of prison rolls, he suggests that it may have had a more oblique role in the story:

The War on Drugs is not increasing admissions directly via the incarceration of drug offenders. But it may be increasing admissions indirectly, by lengthening the records defendants have, and thus the likelihood that prosecutors opt to file charges against them for non-drug crimes. These results may also point to an ongoing collateral cost of the crime boom of the 1960s to the 1990s: by producing cohorts of offenders with longer records, it generated a pool of offenders that may face tougher sanctioning outcome even when all else is constant, thus helping prison populations trend upwards even as crime rates fall.